INFRARED STUDIES ON THE ROTATIONAL ISOMERISM OF 2-CHLOROETHANOL AND 2-BROMOETHANOL

Author Institution: D\'{e}partment de Chimie, Universit\'{e} LavalEnthalpy differences ($\Delta H$) between trans and gauche isomers in the vapor state obtained by relative intensity measurements on the two OH stretching bands of each molecule are higher by 0.45 kcal/mole than those obtained by measurements on the CX stretching bands. This apparent discrepancy is interpreted as due to the existence of a second gauche isomer, the hydroxyl group of which does not participate in an intra-molecular hydrogen bond, and which is less stable than the trans isomer. The relatively high frequencies $(340 cm^{-1})$ of the OH torsional vibrations in the vapor confirm that the most abundant gauche isomer is stabilized by a strong intra-molecular OH {\ldots} X bond. The spectra of the solid reveal that 2-chloroethanol possesses two crystalline phases: a stable phase consisting of molecules in the gauche conformation only, and metastable phase consisting of a mixture of trans and gauche molecules